Power transmission belts for use with toothed pulleys are well known in the art. These belts have a plurality of alternating teeth and grooves extending generally transversely of the belt which mesh with alternating teeth and grooves of the toothed pulley in order to perform their driving function. The most widely used of these toothed belts are the so-called synchronous or positive drive belts which are manufactured from flexible resilient material such as natural or synthetic rubber. These belts are designed and manufactured with pitch, tooth depth, width and other measurements accurate to a precise degree with extremely close tolerances being maintained. Additionally, a high stength tensile stress-resisting member of essentially inextensible material is provided substantially on the dedendum line of the teeth to prevent undue stretching of the belt. This belt costruction allows the flexible resilient belt teeth to mesh without substantial change of pitch with the teeth of the toothed pulleys, with the belt thereby functioning as a synchronizing belt.
It is known to manufacture synchronous belts by placing a layer of fabric intended to cover the teeth and the grooves of the belt, on a grooved cylindrical drum, winding a layer of stress-resisting cord upon the layer of fabric, followed by a layer of elastomeric material on the assembly. The assembly comprising the fabric, the cord layer and the layer of elastomeric material forms a sleeve.
An elastic curing jacket is placed around the above-described sleeve which is assembled on the grooved drum, and the unit is placed in a vulcanizing chamber, to which steam under pressure is admitted. Inside the chamber the molding and curing of the belt is completed by virtue of the action of the heat and of the steam pressure.
Following the molding and curing step, the sleeve is cooled and removed from the grooved drum and individual belts are cut from the sleeve.
It is impractical to manufacture toothed belts having a large circumferential length because, to obtain them, it is necessary to provide metallic grooved drums having a very large diameter, and consequently, of a considerable weight.
Several methods have been proposed to provide synchronous drive belts in lengths greater than are available in the industry. The use of interlocking tongue members to splice the belt ends together is disclosed in U.S. Pat. No. 3,833,998, issued Sept. 10, 1974 to E. G. Tomlinson, and U.S. Pat. No. 3,988,940, issued Nov. 2, 1976 to R. Szonn and R. Breher. Another method for splicing belt comprises embedding the cord ends of two belt sections in rubber to form an endlessly body portion, as disclosed in U.S. Pat. No. 3,419,449, issued Dec. 31, 1968, to P. DiValerio, W. Skura and J. O'Donnell.
The integrity of these spliced areas is relatively poor as compared to the remainder of the belts. In general, spliced belts are rated at only 40% of the standard rated capacity, although higher ratings have been alleged.
With belts which have to run in a precise vibration-free manner, especially at higher speeds, the following conditions are to be met:
1. Homogeneity of the material over the circumferential length of the belt; PA0 2. Uniform cross section; PA0 3. Maintaining the neutral bending line of the cross section; PA0 4. Uniform pull stress behavior of the strength carrier inserts over the total width; PA0 5. Uniform preload of the strength carrier particles over the width of the belt; PA0 6. Merger of the belt material including the reinforcement of the strength carriers at the endless connection without stiffening the bending ability.
Experience has shown that the total of these conditions when an increased quality is required are met primarily by belts with which the strength carriers consist of inserted threads, cables, or the like, which with narrow tolerances concerning the pull stresses and with identical finish tension are located closely adjacent to each other in the same neutral plane.
With fabric and other layer inserts, steps are necessary in order to obtain the precision required for a uniform running behavior of the belt. All heretofore known belts made endless show at the endless area some inhomogeneities which can be ascertained in part already by static tests. The following methods of making belt sections endless are known and have shown the following deficiencies;
a. Overlapping with straight, biased, and offset edge ends according to which the material is cemented, welded or vulcanized. This connection even with spliced ends is usable only for stresses. PA1 b. Connection with stepped layers as they are employed in connection with conveyor belts have a satisfactory uniform run only when also the layer-shaped strength carriers are arranged in stepped manner with regard to each other. This multilayer fabrication is suitable only for heavy belts which, in view of the relatively low running speeds, do not have to meet increased precision requirements with regard to their dynamic behavior. PA1 c. Welding and clamping connections of the strength carrier construction with subsequent overlapping (cementing, welding, or vulcanization, the nonuniformity is always felt particularly during the operation. The liability to disorders increases considerably with decreasing running diameter. PA1 d. Connection by open or exposed special locks. In this instance, the degree of uniformity is particularly felt and a beating noise cannot be avoided. PA1 e. Simple cross-sectional butt connections. These are sometimes prepared in a direction perpendicular to the length but also at an incline thereto, or also in the manner of an arrow. These connections will at any rate cut through the strength carrier elements. The transmitting force is limited by the strength of the belt-forming material. PA1 f. The teeth-like interengagement with butt connection of the edges. While this connection results in a considerable extension of the interconnected edges, it will be appreciated that also in this instance the strength elements are cut through one after another. The respective only short offset arrangement does not result in any material strength transfer between the belt material and the strength carriers. Therefore, a considerably reduced transmitting force will result with belts made endless in this manner.
It is, therefore, an object of the present invention to provide a transmission belt which will overcome the above-mentioned drawbacks.
It is another object to provide a method for making an improved synchronous power transmission belt.
Other objects and advantages of the present invention will appear more clearly from the following specification, the appended claims and the accompanying drawings.